Asthma is a chronic inflammatory disorder of the airways. Whilst inflammation is a natural feature in the lungs of healthy individuals, for example to effect the removal of pathogens such as bacteria and viruses and pollutants which are present in the air, in the asthmatic lung an exaggerated response occurs in response to irritants (hyperresponsiveness). Increased airway inflammation follows exposure to inducers such as allergens, viruses, exercise, or non-specific irritant inhalation. Increased inflammation leads to exacerbations characterized by shortness of breath, chest tightness, wheezing, coughing, and dyspnoea.
Asthma is the most widespread chronic health problem in the Western world and is increasing in prevalence around the world. In Australia alone, it affects over 2 million individuals. Worldwide bronchial asthma is the most common chronic disease in childhood with an overall prevalence between 5 and 20 percent across all ages. The pathogenesis is suggested to be complex and is centred on an aberrant immune response to inhalant allergens, most commonly house dust mite (HDM) allergens, that results in an inflammation of the airway wall together with an episodic constriction of the airways resulting in symptoms such as shortness of breath, wheezing, coughing, and life-threatening dyspnoea.
Current asthma therapies typically aim to reduce the inflammatory process by suppressing the expression of steroid-sensitive proteins via systemic or local application of corticosteroids, by inhibiting the action of leukotrienes via systemic application of leukotriene receptor/leukotriene antagonists, or by neutralising immunoglobulin E (IgE) or interleukin-5 (IL-5) via systemic application of antibodies directed against these molecules (these therapies are commonly referred as “preventers”). Alternative current therapies aim to inhibit the constriction of airways by stimulating beta-2 receptors in the airways via short or long-acting beta-2 receptor agonists (“relievers” and “controllers” respectively).
However these existing therapies do not address the complex nature of the pathways that are activated in the airways during asthma on a molecular level. Rather they aim to either suppress only one or a few out of numerous disease mechanisms that promote aberrant immune responses or alleviate symptoms only. Furthermore current therapies are commonly associated with significant side effects (for example in the case of steroid use) or tachyphylaxis (for example following administration of long-acting beta-2 receptor antagonists).
Accordingly, there remains a clear need for the development of effective therapies for the treatment of inflammatory conditions such as asthma. There is also an ongoing need to pursue asthma-related research at the level of both understanding underlying causative factors, identifying novel therapeutic targets and developing new treatment, regimens, which can contribute to expanding the existing range of therapeutic and prophylactic treatments available.
MicroRNAs (miRNAs) are an abundant class of small endogenous non-coding RNA molecules that have been highly conserved through evolution. Indeed, in mammalian species, 100% conservation of many miRNA sequences is observed between humans and mice. More than 1000 miRNAs have been identified to date, and approximately 400 miRNAs with known sequence have been found in humans. miRNAs are believed to play an important role in regulating gene expression. Each miRNA binds incompletely to its cognate target messenger RNA (mRNA) and as such each miRNA may bind to and potentially regulate many target mRNAs. Computational analysis suggests that there may be several hundred mRNA targets for any given miRNA. Accordingly, a unique miRNA may regulate the expression of several hundred mRNAs each of which codes for a specific protein. It is suggested that miRNAs may regulate the expression of up to one third of all human genes that code for an unique protein.
Mature miRNAs are derived from so-called pri-miRNAs that are transcribed from regions of non-coding DNA. Pri-miRNAs, usually containing several hundred nucleotides, are processed into stem-loop precursors (pre-miRNAs) of approximately 70 nucleotides by RNase III endonuclease. Pre-miRNAs are actively transported into the cytoplasm where they are further processed into short RNA duplexes, typically of 21-23 bp. The functional miRNA strand dissociates from its complementary non-functional strand and locates within the RNA-induced-silencing-complex (RISC). (Alternatively, RISC can directly load pre-miRNA hairpin structures.) The miRNA-RISC complex incompletely binds to its cognate mRNA target through a small region at the 5′ end. miRNA-induced regulation of gene expression is then typically achieved by translational repression, either degrading proteins as they emerge from ribosomes or ‘freezing’ ribosomes, and/or promoting the movement of target mRNAs into sites of RNA destruction.
The roles of miRNAs have yet be completely elucidated. However they appear to be important in a number of developmental processes, for example in differentiation and maintenance of cellular identity in hematopoiesis, in establishing muscle phenotypes, in morphogenesis of epithelial tissues, organogenesis and in other metabolic processes. Additionally, specific miRNAs are increasingly being implicated in disease conditions, including cancers such as chronic lymphocytic leukemia (Calin, G. A. et al., 2005, N Engl J Med 354:524-525).
The present invention is predicated on the inventors' surprising finding that expression of a subset of miRNAs is upregulated or downregulated in response to allergen challenge and the finding that a modified antisense oligonucleotide specific for an upregulated miRNA is able to suppress hallmark features of allergic airways disease. Accordingly, the present invention opens avenues for novel therapeutic approaches to the treatment of allergic and inflammatory disorders.